The mechanisms controlling successful reproduction in hamsters mediate a complex interplay of physiological responses and behavior. Sexual stimulation is necessary for the induction of the neuroendocrine reflex that prepares the uterus for the implantation of the fertilized ova, the progestational state, and for the cooperative mating behavior of the female with the male. This is an investigation of the key brain regions mediating this neuroendocrine reflex and the mechanism by which the female uses stimulation from the male to modify her behavior during mating. An anterograde transneuronal viral tracing study from the vaginocervical area to the brain will highlight brain regions that can be activated by intromissive stimulation from the male. To test the critical involvement of selected individual sites, a lesion study that incorporates a compact cascade of tests with possible outcomes and predetermined interpretations will evaluate each selected site for its role in the induction of the progestational state and in the reinforcing effects of mating. This approach will integrate mating stimuli with the neural control of behavior and physiological responses relevant to reproduction.